The goals of the proposed research include (a) the characterization and partial purification of rat lung fatty acid synthesizing enzymes and phospholipid; (b) the study of variations in the total activities of these enzymes in diabetic, hypophysectomized and adrenalectomized animals and to determine the effect of insulin, triiodothyronine and corticosteroids respectively in the hormonally deficient states; (c) to determine the effect of various diets (high saturated fat-low carbohydrate, high unsaturated fat-low carbohydrate, and fat free high carbohydrate) on the total activities of the above enzymes. These studies are designed to measure the optimum fatty acid synthesizing capacity of the rat lung and to determine its contribution towards surfactant synthesis. A modification of the fatty acid composition of lipid stores in conjunction with depressed saturated fatty acid synthesis (diabetic state) could lead to altered composition of surfactant provided the plasma fatty acids are the major source of surfactant phospholipid. This will not be the case if surfactant fatty acids are derived mainly from de novo synthesis in the lung. The effect of corticosteroids on the possible enhancement of fatty acid and phospholipid synthesizing capacity of rat lungs of adrenalectomized animals is designed to elucidate the role that the steroids might play in the control of surfactant accumulation in fetal lung. The amounts of various lung enzymes in the nutritionally altered or hormonally deficient states will be quantitated by antigen-antibody titration. Antibodies to purified rat liver enzymes will be used in these studies.